psalm/docs/running_psalm/issues/UnusedParam.md

UnusedParam

Emitted when --find-dead-code is turned on and Psalm cannot find any uses of a particular parameter in a private method or function

<?php

function foo(int $a, int $b) : int {
    return $a + 4;
}

Can be suppressed by prefixing the parameter name with an underscore:

function foo(int $_a, int $b) : int {
    return $b + 4;
}